I posted it in another thread, but Jim Fey's "Love and Logic" approach,
http://www.loveandlogic.com/ , stresses
consequences over
discipline, which to me makes more sense, since the idea is to train your child to eventually cope in an adult world where there are consequences for your actions.
And no, there is no age too young to start. The trick is to make the
consequences age appropriate so that the child can understand that when he/she does
a, then
b happens, and that they really don't like
b so they choose not to do
a.